Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read may be referred to as “read heads” herein, regardless of other devices or functions that the read head may also include or perform (e.g. writing, flying height control, touch down detection, lapping control, etc).
The typical magnetic hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The HDA includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The spindle motor typically includes a rotating hub on which disks are mounted and clamped, a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle motor, for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The HSA typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes and supports the read head for reading and writing data from and to the disk. In magnetic recording applications, the read head typically includes an air bearing slider and a magnetic transducer. The magnetic transducer typically comprises a magneto-resistive read element (e.g. so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element), and an inductive write structure comprising a flat coil deposited by photolithography, and a yoke structure having pole tips that face a disk media. In optical and magneto-optical recording applications, the read head may include a minor and an objective lens for focusing laser light on an adjacent disk surface.
During operation of the disk drive, the actuator must rotate to position the heads adjacent desired information tracks on the disk. The actuator includes a pivot bearing cartridge to facilitate such rotational positioning. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator. A crash stop is typically provided to limit rotation of the actuator in a given direction, and a latch is typically provided to prevent rotation of the actuator when the disk drive is not in use.
The HGA typically also includes a head suspension assembly that includes a mounting plate, a load beam, and a laminated flexure to carry the electrical signals to and from the read head. The read head is typically bonded to a tongue feature of the laminated flexure. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, a rotary actuator, and a flex cable. The mounting plate of each head suspension assembly is attached to an arm of the rotary actuator (e.g. by swaging), and each of the laminated flexures includes a flexure tail that is electrically connected to the HSA's flex cable (e.g. by solder reflow bonding or ultrasonic bonding).
Modern laminated flexures typically include electrically conductive copper traces that are isolated from a stainless steel support layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flex cable on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along the actuator arm and ultimately attaches to the flex cable adjacent the actuator body. That is, the flexure includes electrically conductive traces that are electrically connected to a plurality of electrically conductive bonding pads on the head (e.g. by gold ball bonding), and extend from adjacent the head to terminate at electrical connection points at the flexure tail.
Most modern HDAs include a ramp adjacent the disk outer periphery. In such HDAs, each HGA (itself attached to the distal end of an actuator arm in the HSA) typically includes a lift-tab. The lift-tab is designed to contact a lift-tab supporting surface of the ramp when the actuator moves near an extreme position that is typically beyond the disk outer periphery. To prevent the heads from sliding off of the outer edge of the disk before they are properly unloaded, a portion of the ramp (that includes a portion of the lift-tab supporting surface) typically must extend over the disk outer periphery. That portion of the ramp overlaps the disk in a region of the outer diameter that includes a head landing zone. The head landing zone typically does not include user data, because contact with the ramp and/or disk in the head landing zone typically prevents the head from reliably reading and writing data there.
Typically at the beginning of a period when the disk drive is not in use, the actuator rotates the HSA so that each HGA's lift-tab contacts a corresponding lift-tab supporting surface, in a lift-tab pick-up region of that lift-tab supporting surface, to unload the heads from the surface of the disk. Then the actuator continues to rotate so that each of the lift-tabs slides over the lift-tab supporting surface to a lift-tab parking region where it will remain while the disk drive is not in use. The position of the HSA when the lift-tabs are in the lift-tab parking region is referred to as the parked position of the HSA.
The benefits of unloading the heads can include improved tribological performance and reliability of the head-disk interface and improved robustness to mechanical shocks that are suffered under non-operating conditions. Contemporary disk drives are designed to withstand and survive greater mechanical shocks during non-operation, than during operation. For example, the disk drive is more sensitive during operation because the fragile heads are then spaced very close to the fragile and fast moving surfaces of the magnetic disks. During non-operation, however, the fragile heads are unloaded from the surfaces of the magnetic disks, with the HGAs “parked” on a nearby ramp. Therefore, the heads are less likely to impact and thereby damage the disk surface in response to mechanical shocks when the HSA is in the parked positions.
Some mechanical shocks during non-operation may be severe. For example, a HGA may experience mechanical shock or vibration when the host system in which the disk drive is mounted is dropped or impacted. An HGA may experience an even greater mechanical shock if the disk drive is dropped or impacted before it is enclosed in a host system. When impacting a hard surface, the accelerations resulting from the mechanical shock can have a greater amplitude (and shorter duration) than when impacting a softer surface. In some cases, severe shocks can cause cracking of the electrical connections between the read head and the conductive traces of the HGA flexure, with such cracks often beginning at the locations of the maximum stress experienced by such electrical connections during a mechanical shock event. Such cracks can cause a complete failure of disk drive operation and result in catastrophic data loss.
Typical expectations and specifications for mechanical shock robustness in the disk drive industry are becoming more stringent and challenging, especially for disk drives designed for mobile applications. To meet such specifications the disk drive must be able to survive more severe mechanical shocks during non-operation than ever before. Thus, there is a need in the art for a HGA design having an improved structure for limiting head deflection in response to mechanical shocks that may occur under non-operating conditions, and/or reducing the maximum stress at read head electrical connections during such mechanical shocks.